Photoelectric exposure meter having connected movable galvanometer and calculator scales



Sept. 13, 1949. J, MIHALY. 2,481,678

PHOTOELECTRIC EXPOSURE METER HAVING CONNECTED MOVABLE GALVANOMETER ANDCALCULATOR SCALES Filed March 14, 1946 2 Sheets-Sheet 1 FIG.2. I FIG.1.

J QSEPH MIHALYI INVENTOR' Sept. 13, 1949. J. MIHALYI 2,481,678

PHOTOELECTRIC EXPOSURE METER HAVING CONNECTED MOVABLE GALVANOMETER ANDCALCULATOR SCALES Filed March 14, 1946 2 Sheets-Sheet 2 PH: 5 iii JOSEPHMIHALYI 37 g :i! INVENTOR 6 I a: 1:! WW

1 HF J-LU A TTORNE 5 Patented Sept. 13, 1949 UNITED STATES PATENT orrlcsPHOTOELECTRIC EXPOSURE METER HAV- ING CONNECTED MOVABLE GALVANOM- ETEBCALCULATOR SCADES Joseph Mihalyi,- Rochester, N. Y., assignor to EastmanKodak Company, Rochester, N. Y., a corporation of New Jersey ApplicationMarch 14, 1946, Serial No. 654,32!

1 Claim. (01. 88-23) the reading of the meter itself merely providingthe unknown value. The inability to make these meters read directly hasbeen due to the fact that the greater output of the light-sensitivecell, which output is linearly proportional to the light striking it,the smaller should he the aperture opening to give the same exposure tothe film. However, the stops on a camera are in geometrical ratio, eachsmaller sto transmitting one-half the light of the previous stop. Thus,at low levels of illumination, even a small linear change in intensityrequires a large change in aperture.

One object of the present invention is the provision of a photoelectricexposure meter which will read directly in diaphragm stop values so thatno calculation is necessary.

Another object is to provide an exposure meter the pointer of which hasa substantially linear response which makes possible the use of a meterscale which comprises f-values evenly spaced there-along.

A further object is they provision of a meter of the type set forthwherein the f-scale is auto-r matically adjusted in accordance with filmspeeds and/or shutter speed combinations.

The novel features that I consider characteristic of my invention areset forth with particularity in the appended claim. The invention,itself, however, both as to its organization and methods of operation,together with additional objects and advantages thereof, will best beunderstood from the following description when read in connection withthe accompanying drawings in which,

Fig. l is a front elevational view or exposure meter constructed inaccordance with a preferred embodiment of the present invention,

Fig. 2 is an enlarged vertical section taken substantially on line 2-2of Fig. 1,

Fig. 3 is a horizontal section taken substantially on line 33 of Fig. 2,

Fig. 4 is a perspective view of the meter with certain parts broken awayto show the arrangement and cooperation of the Parts,

Fig. 5 is a view showing the meter connected I to the top of a cinecamera so that the diaphragm scale on the camera lens can be viewed fromthe view finder position of the camera.

Fig. 6 is a view showing how the meter will appear to the photographerfrom the rear, or view finder position, of a camera, and

Fig. 7 shows a modification of the meter which uses two mirrors insteadof one for directing an image of the diaphragm scale on the camera lensto the view finder position so that the scale numbers appear right sideto, and so that different focal length lenses may be accommodated.

Like reference characters refer to corresponding parts. throughout thedrawing.

Referring now to the drawings, the proposed exposure meter is containedin a plastic casing it, made up of a body portion forming a front wallti, and a cover forming a rear wall i 2 parallel to and spaced from thefront wall. Mounted within this casing is a conventional light-seashtivecell l3 covered by a molded window l4 made from a, transparent plasticor glass. Connected to and operated by the light-sensitive cell is amoving coil instrument, or galvanometer consisting of a magnet l5 andcoil it which is pivotally mounted in the'magnet field by a bracket ii.

To the coil I6 is attached the curved pointerwhich passes beneath, andat the focal point of, a cylindrical lens l9 cemented to the glasswindow 20, located in the rear wall of the meter. The image 2! of thepointer ill from the cylindrical lens reads on the diaphragm stop scale22 etched on the metal band or tape 23. This tape is wrapped aroundrollers, not shown, at each side of the casing so that it is free tomove back and forth. The tape is positively actuated by gear 24 whichmeshes with gear teeth 25 cut in the edge of the tape (see Fig. i)

Gear 24 is fixed to shaft 26. extending through the rear wall of thecasing and is turned by knob 27. Fixed rigidly to shaft '26 is the filmspeed disk 28 with the various emulsion speeds etched on the facethereof. Friction held to the same shaft is the window disk 29 throughthe window 29' of which the emulsion speeds on disk 28 and a'shutterspeed scale 39, molded on the front' stop values, due to making thef-aperture values equally spaced on the tape 23. The even spacing of thef-values is accomplished by the combined use of three difl'erentfeatures. First, the pivot point of a coil it that carries the pointerI8 is set off to the end of the meter scale nearest the smallestaperture value. Thus, the sensitivity of the device at wide aperturereadings is relatively magnified compared to the rest of the scale. Thisfeature is completely disclosed in my U. S. Patent 2,358,083, whichissued September 12, 1944, and to which reference can be had for a morecomplete discussion as to how this particular location of the pivot ofthe pointer tends to make the response of the meter a substantiallylinear one.

So locating the pivot of the pointer does not render the movement of thepointer absolutely linear in response to permit equal spacing of thef-values on the scale, but leaves slight irregularities which can betolerated although they are undesirable. These irregularities arefurther smoothed out by curving the pointer l8 as shown, and using acylindrical lens I! for forming an anastigmat image 2| of only a singlepoint there of. Just how and why a bent pointer moving over a straight,narrow slit, which is what the cylindrical lens It provides, willovercome different angular movements of the meter pointer is fullydisclosed in my U. S. Patent 2.358.084, which issued September 12, 1944.It will suflice here to say that the bent pointer in combination withthe cylindrical lens acts to overcome any irregularities in movement ofthe pointer not eliminated by the special disposition of the pivot pointthereof to the one end of the diaphragm scale, and, hence. the cellresponse is rendered truly linear so that a diaphragm scale havingequally spaced f-values can be used.

Mounted in the front wall ll, directly in line with the opening in thecenter of magnet I5, is a weak positive, or reading, lens 3|, which incombination with window 32 in the rear wall of the casing forms a sightopening through the casing. Pivotally mounted at .33 on the front wallis a cover plate 3|. which moves between a lowered position, see Fig. 2,wherein it covers lens 3|, and a raised position, see Fig. 5, and dottedline position in Fig. 2. A mirror 35 is fastened to the underside of thecover late 34. The bottom of the meter is provided with a conventionalaccessory clip button 15 which is adapted to he sli ped into anaccessory clip 46 mounted on the top of the combined range and viewfinder housing H of a cine camera. see Fi 5. When the meter is so.mounted on the camera. and the cover plate 34 is raised a magnified viewof the diaphragm scale 36 on the camera lens 31 can be seen from theview finder position and can be paired with the correct value as givenby the meter. The diaphragm of the camera lens can, therefore. bereadily adiusted in accordance with the meter reading withoutnecessltating removal of the camera from in front of the photographer'seye. In Fig. 6 I have shown how the meter and view-finder field wouldappear to the user from the rear of the camera.

The use of a single mirror 35 will cause the numbers of the diaphragmscale and lens to appear in reverse, or 16 will appear as 61, etc.Although such f-values are so well known to photographers that theirappearance in reverse would probably not be too confusing, it might bewell to correct this defect. This can readily the single mirror isreplaced by a pair of pivoted mirrors and ll. The mirror will nowreflect the image of the diaphragm scale on the lens onto the othermirror II, which will in turn reflect it through the sight opening inthe meter casing. This second mirror II will reverse the image reflectedby and reversed by mirror 35 so that the scale readings as viewed willbe right end to. The view shown in the window I! of Fi 6 is through thismirror arrangement of Fig. 7. This combination of two mirrors offers theadded advantage that lenses of diii'erent focal lengths can beaccommodated. since by relatively adjusting the mirrors the diaphragmscale of a long focal length lens, which extends a substantial distancefrom the front wall of the camera, can be reflected through the sightopening in the casing as well as the scale on a short focal length lens,see Fig. 7. The pivots of the mirrors will possess sufficient frictionto hold the mirrorsin adjusted position, and the mirrors of Fig. 7 areadapted to close in superimposed relation on the front wall of thecasing and in covering relation with the lens ll.

The operation of this exposure meter is as follows. Assuming that ashutter speed of 100 andafilmspeedof24is tobeused, thewindow 28 inwindow disk 29 is set to the shutter speed of 100 by rotating the disk1!, and the film speed 24 is then set in the window I! by rotating theknob-21 to which is fastened the film speed disk 28. During this lastoperation the window disk 28 is held from turning by the operatorgripping the pins P thereon. In setting the film speed disk 2. gear 24is rotated to move the tape 23 through the teeth 2! cut in the edgethereof. In this manner the location of the faperture scale 22 is movedlongitudinally relative to the meter pointer.

40 After the correct setting has been made, the

exposure meter is held up so that light from the object to bephotographed enters the window I and excites the light-sensitive cell Itwhich then sends a flow of current to the ma net and I creates amagnetic field at gap between the poles of magnet. Since the coil It ispivotally suspended in this magnetic field, the field will tend to makethe coil rotate, the amount of the rotation depending on the strength ofthe field.

'0 When coll It rotates, it carries with it pointer is which is sopositioned that it passes beneath the lens I! at its focal point. Theimage of the point on the pointer is the line II which reads on thef-aperture scale 22. The pointer is ll so pivoted with reference to thef-aperture scale, and the pointer is bent, so that it translates theresponse of the cell and the galvanometer into a straight-linerelationship, thus making it possible to evenly space the f-aperture Nvalues on the scale 22 along the tape 23. In other image of a singlepoint on the pointer which results in the definite line image II to readagainst the scale 22.

If the meter is set as shown in Fig. 6 with a film emulsion speed of 24and a shutter speed of 100, the correct diaphragm opening is f/4 as seenby the position of line H relative to the diaphragm scale 22. Supposingthat the film was changed to one of an emulsion speed of, say 48. To setthis new film speed, window disk 2! be done by the modification shown inFig.7where is held against movement by gripping pins P and knob 21 isturned counterclockwise so that number 48 appears in the window 28 Theshutter speed setting is still 100. As the knob 21 is turned, gear 24turns also and moves the tape 23 to the right bringing the f-value 5.6over the image 2| oi the pointer, thus making f/5.6 the correctdiaphragm opening for the existing conditions. .These settings are shownin Fig. 1.

Now suppose that it is desirable to change the shutter speedto 50. Againthe knob 2'! is turned counter-clockwise and the window disk 29 isallowed to rotate with it. Film speed value stays fixed to the window 29as 48, but the window moves past the stationary shutter speed scale 30until it uncovers the desired shutter speed 50. As before the gear 24turns with knob 21 and moves the f-aperture tape 23 to the right untilthe i value 8 is above the pointer image 2|. Now the film speed is 48,the shutter speed is 50 and the correct f-value is 8. Assuming that thesame light intensity exists as did when, at the start, the film speedwas 24, the shutter speed 100 and the f-aperture was 8, it follows thatthe last-arrived at f-value is correct since doubling the film speed andhalving the shutter speed cuts down the diaphragm aperture by two stops.

For use on cine cameras, see Figs. 5, 6, and

7, the meter is mounted on the top of the finder housing H oi the camera30 so that the f-aperture scale 36 on the lens 31 can be read from theview finder position. To read the f-aperture scale 38 on the lens, themirror 35 in Fig. 5, or the mirrors 3! and I in Fig. 7, are raised untilthe image of the scale 36 on the camera lens is reflected through theweak lens 3| and so through the window 32 to the observer's eye which isat the view finder position. The two aperture scales are now positionedon above the other, see Fig. 6, and can be read at the same time so thatthe correct diaphragm stop value can be taken from scale 22 andtransferred to the lens 31 by rotating the lens diaphragm scale untilthe correct stop value, the image in window 32, is opposite the image llof the index on the f-aperture scale on the lens. The f-aperture of thecamera lens 31 can be properly set without moving the camera from thepicturetaking position.

Although I have shown and described certain specific embodiments oi myinvention, I am fully aware that many modifications thereof arepossible. My invention, therefore, is not to be limited to the precisedetails oi construction shown and described. but is intended to coverall modifications coming within the scope of the appended claim.

Having thus described my invention, what I claim is new and desire tosecure by Letters Patent 01 the United States is:

An exposure meter comprising in combination a casing; a light-sensitivecell in said casing; a galvanometer in said casing including a pointerand connected to and operated by said cell; a tape movably supported insaid casing to move longitudinally in the plane 0! movement of thegalvanometer pointer; a galvanometer scale on said tape and labeled inlens aperture units, and consisting of a row of individual markssubstantially evenly spaced longitudinally of said tape along which thegalvanometer pointer moves; said pointer being curved to cause it tomove substantially linearly along said scale in response to the outputof said cell; means for adjusting said tape, including a manuallyadjustable rotatable member having its axis parallel to the axis of thepointer and having a positive drive connection with said tape; a fixedarcuate scale and a movable arcuate scale mounted in adjacentrelationship on said casing and having the same axis as the adjustablemember, one of said scales calibrated in shutter speeds and the other infilm speeds; means for positively connecting said movable scale to saidadjustable member whereby said movable scale is moved relative to saidfixed scale and said tape is moved longitudinally when said manuallyadjustable member is moved; a movable rotatable plate having the sameaxis as the adjustable member in covering relation with said two scales,and including a window of such size and disposition as to uncoversimultaneously one calibration on each of said scales in any givenposition of adjustment. of said plate; means for frictionally connectingsaid plate to said manually adjustable member so that it will normallybe moved with said member; and means for selectively holding said plateagainst movement as said adjustable member is moved, whereby said tapeand the scale thereon can be adjusted in accordance with any combinationof shutter speed and film speed.

JOSEPH MIHALYL REFERENCES CITED The following references are of recordin the file of this patent:

UNITED STATES PATENTS Number Name Date 1,620,727 Howell Mar. 15, 19272,070,664 Kuppenbender Feb. 16, 1937 2,076,481 Riszdorfer Apr. 6, 19372,105,255 Mihalyi et al. Jan. 11, 1938 2,245,522 Bernhard et a1. June10, 1941 2,247,763 Meyers July 1, 1941 2,358,083 Mihalyi Sept. 12, 19442,358,084 Mihalyi Sept. 12, 1944 2,360,256 Mihalyi Oct. 10, 1944

